Quantum algorithm for Feynman loop integrals.

We present the first flagship application of a quantum algorithm to Feynman loop integrals. The two on-shell states of a Feynman propagator are identified with the two states of a qubit and a quantum algorithm is used to unfold the causal singular configurations of multiloop Feynman diagrams. Since the number of causal states to be identified is nearly half of the total number of states in most cases, an efficient modification of Grover's algorithm is introduced, requiring only ${\cal O}(1)$ iterations. The output of the quantum algorithm in the IBM quantum simulator is used to bootstrap the causal representation in the loop-tree duality of representative multiloop topologies. The algorithm may also find application and interest in graph theory to solve problems involving directed acyclic graphs.